Various methods are known for the separation of air into its constituent predominant gas compositions, namely; oxygen and nitrogen. In U.S. Pat. No. 4,132,766 a process is set forth wherein air is separated into an oxygen product and a nitrogen-rich waste stream utilizing an oxygen acceptor composition comprising the alkali metal nitrate and nitrite salts which will reversibly absorb oxygen differentially over nitrogen from air. It is noted in that patent that the nitrates will decompose into the superoxides and that nitrogen and oxygen will form resulting nitrogen oxides during the absorption process.
In U.S. Pat. No. 4,287,170, a process is set forth for the chemical separation of air into both oxygen and nitrogen wherein the nitrogen is further purified of any trace oxygen by passage through an oxygen scavenger such as manganese oxide. The process discloses that the nitrate to nitrite ratio is between 5 and 20 and the molten salt additionally has at least 1% total dissolved oxides such as peroxides and superoxides.
Finally in U.S. Pat. No. 4,340,578 another chemical air separation process is set forth wherein the molten salt oxygen acceptor comprises a cation composition of sodium and potassium cations and an anion composition of 50 to 94% nitrate, 4 to 25% nitrite and 2 to 25% combined peroxide and superoxide. The patent specifically desired that the oxide concentration is above 2% in order to effectively catalyze the oxygen uptake of the absorber or acceptor, reduce the nitrogen oxide levels and avoid highly corrosive conditions. It is preferred to operate near the 2% minimum concentration set forth in the patent.
The present invention overcomes the drawbacks of nitrogen oxide formation, inactivity of the oxygen acceptor and corrosiveness of the salt composition with an improved composition which effectively provides good separation of oxygen from air.